That depends, there are a lot of different mindsets when playing magic. People buy boosters to pop open packs to gamble on a big card, or people just buy the stuff they need.
Personally, I draft a lot (too much) and by doing so I get free boosters when I win, cutting th costs of future drafting. From doing this, I have gotten enough in picking high price cards I got 2 decks going. Tempered Steel and Inkmoth Infect. Iv'e been playing for around 2 weeks.
You're friends don't HAVE to buy their collection again, you can use MTGO to your liking.